An infra-red search and track system is a method for detecting and tracking
objects which give off infrared radiation such as jet aircraft and
helicopters. IRST is a generalized case of forward
looking infrared, i.e. from forward-looking to all-round situation
awareness. Such systems are passive, meaning they do not give out any
radiation of their own, unlike radar. This gives them the advantage that they
are difficult to detect. However, because the atmosphere
attenuates infra-red to some extent and because adverse weather can attenuate it
also, the range compared to a radar is limited. Angular resolution at short
ranges is better than radar due to the shorter wavelength.
Early systems The first use of an IRST system appears
to be the F-101 Voodoo, F-102 Delta Dagger and F-106 Delta Dart
interceptors. The F-106 had an early IRST mounting replaced in 1963 with a
production retractable mount. The IRST was also incorporated into the Vought
F-8 Crusader which allowed passive tracking of heat emissions and was
similar to the later Texas Instruments AAA-4 installed on early F-4 Phantoms.
The F-4 Phantom had a Texas Instruments AAA-4 infrared seeker under the nose of
early production aircraft F-4B's and F-4C's and not installed on later
F-4-D's due to limited capabilities, but retained the bulge and indeed some
F-4D's had the IRST receiver retrofitted in a modified form.
The F-4E eliminated the AAA-4 IRST bulge and received an internal gun mount which
took up the area under the nose. The F-4J also eliminated the AAA-4 IRST
receiver and bulge under the nose. The Swedish Saab J-35F2 Draken also used
an IRST, a Hughes Aircraft Company N71. = Technology =
These were fairly simple systems consisting of an infra-red sensor with a
horizontally rotating shutter in front of it. The shutter was slaved to a
display under the main interception radar display in the cockpit, any IR
light falling on the sensor would generate a "pip" on the display, in a
fashion similar to the B-scopes used on early radars.
The display was primarily intended to allow the radar operator to manually
turn the radar to the approximate angle of the target, in an era when radar
systems had to be "locked on" by hand. The system was considered to be of
limited utility, and with the introduction of more automated radars
they disappeared from fighter designs for some time.
Later systems IRST systems re-appeared on more modern
designs starting in the 1980s with the introduction of 2-D sensors, which cued
both horizontal and vertical angle. Sensitivities were also greatly
improved, leading to better resolution and range. In more recent years, new
systems have entered the market. In 2015, Northrop Grumman introduced its
OpenPod(TM) IRST pod, which uses a sensor by Selex ES.
The best known users of modern IRST systems are:
Russia Su-27 Flanker
Mikoyan MiG-29 Sukhoi PAK FA
United States Grumman F-14 Tomcat
Lockheed Martin F-16 E/F Block 60/62 Boeing FF Super Hornet
Lockheed Martin F-35 Lightning II AN/AAQ-37 electro-optical Distributed
Aperture System with a 360 degree IRST, missile detection/warning, and day/night
vision capabilities, designed and produced by Northrop Grumman Electronic
Systems. Sweden
Saab JAS 39 Gripen E/F United Kingdom / Germany / Italy /
Spain Eurofighter Typhoon
France Dassault Rafale
These aircraft carry the IRST systems for use in lieu of their radars when the
situation warrants it, such as when shadowing other aircraft or under the
control of Airborne Early Warning and Control(AWACS) aircraft or
Ground-controlled interception(GCI), where an external radar is being used to
help vector them onto a target and the IRST is used to pick up and track the
target once they are in range. With infrared homing or fire-and-forget
missiles, the aircraft may be able to fire upon the targets without having to
turn their radar sets on at all. Otherwise, they can turn the radar on
and achieve a lock immediately before firing if desired. They could also close
to within cannon range and engage that way.
Whether or not they use their radar, the IRST system can still allow them to
launch a surprise attack. An IRST system may also have a regular
magnified optical sight slaved to it, to help the IRST-equipped aircraft identify
the target at long range. As opposed to an ordinary forward looking infrared
system, an IRST system will actually scan the space around the aircraft
similarly to the way in which mechanically steered radars work. The
exception to the scanning technique is the F-35 JSF's DAS, which stares in all
directions simultaneously, and automatically detects and declares
aircraft and missiles in all directions, without a limit to the number of targets
simultaneously tracked. When they find one or more potential
targets they will alert the pilot(s) and display the location of each target
relative to the aircraft on a screen, much like a radar. Again similarly to
the way a radar works, the operator can tell the IRST to track a particular
target of interest, once it has been identified, or scan in a particular
direction if a target is believed to be there.
IRST systems can incorporate laser rangefinders in order to provide full
fire-control solutions for cannon fire or launching missiles. The combination
of an atmospheric propagation model, the apparent surface of the target, and
target motion analysis IRST can calculate the range.
Performance Detection range varies with
clouds altitude
air temperature target's attitude
target's speed The higher the altitude, the less dense
the atmosphere and the less infrared radiation it absorbs - especially at
longer wavelengths. The effect of reduction in friction between air and
aircraft does not compensate the better transmission of infrared radiation.
Therefore, infrared detection ranges are longer at high altitudes.
At high altitudes, temperatures range from −30 to −50 °C - which provide
better contrast between aircraft temperature and background temperature.
The Eurofighter Typhoon's PIRATE IRST can detect subsonic fighters from 50 km
from front and 90 km from rear - the larger value being the consequence of
directly observing the engine exhaust, with an even greater increase being
possible if the target uses afterburners.
The range at which a target can be sufficiently confidently identified to
decide on weapon release is significantly inferior to the detection
range - manufacturers have claimed it is about 65% of detection range.
See also Electro-Optical Targeting System
AN/AAQ-37 Electro-Optical Distributed Aperture System
References = Notes =
= Citations = = Bibliography =
Eden, Paul ed. The Encyclopedia of Modern Military Aircraft. London: Amber
Books Ltd, 2004. ISBN 1-904687-84-9 Kinzey, Bert. F-106 Delta Dart, in
Detail & Scale. Fallbrook, CA: Aero Publishers, 1983. ISBN 0-8168-5027-5.
Sweetman, Bill and Bonds, Ray. The Great Book of Modern Warplanes. New York, New
York: Crown Publishers, 1987. ISBN 0-517-63367-1
External links Fraunhofer Institut IAF annual report
2006 German and English.